Prior art large caliber cannon systems, such as the 155 mm, XM297, frequently experience chamber pressures between 5,000 and 25,000 psi with pressure impulse of 25 milliseconds. The XM297 utilizes a split wedge breechblock with a retentive bridge seal. This breechblock obturator has been described in the U.S. Pat. No. 5,589,656.
The problem with the aforementioned prior art retentive bridge seal was that it had a very short useful life. Post-firing residue buildup on the bridge seal necessitated the bridge seal to be removed from the breechblock and cleaned after each firing in order to insure continued performance of the gun and safety of the gun crew. Such rigid maintenance requirements under combat conditions would not be feasible, and severely limit the prior art gun system's effectiveness.
The present invention eliminates the necessity of frequently cleaning the breechblock obturator retentive bridge seal while retaining the advantages of the split/wedge breechblock concept.